> In general, that argument is that there shouldn’t be any simple technology that would make humans dramatically smarter, since if there was, then evolution would have already found it.
With technology we have massively extended lifespan, so does this argument really hold valid ?
On average. But it wasn't that uncommon to have people reach 100 years of age even 500 years ago. The biggest impact on lifespans was hygiene not medicine (except for maybe anti-biotics).
Vaccines dramatically reduce childhood mortality significantly skewing mortality figures.
For this reason, "life expectancy" doesn't tell you much. "Life expectancy at age 5" tells much, much more about how adults fare.
Evolution is multidimensional, if for improving one trait you diminish another that may for our survival some compromise will be reached. Not by design, but natural selection, at the end matters that the genes manage to survive. If living more implies that against food scarcity you get no surviving children that is the end of the line for the genes that enabled that extra lifespan.
And in evolutionary terms, having agriculture, civilization, technology and a global culture that may support those traits is the exception not the rule.
The word simple does a lot of work here.